1. Field of the Invention
The present invention relates to a magnet for an axial gap dynamo-electric machine.
2. Description of the Related Art
Dynamo-electric machines have been used as drive sources in electric motorcycles or for other general electric motors. In recent years, use of an axial gap dynamo-electric machine as well as a radial gap dynamo-electric machine has attracted the public eye.
For example, an axial gap electric motor such as an axial gap dynamo-electric machine, has a disk shaped rotor yoke with a revolving shaft supported by a bearing thereof. A stator yoke has a laminated body in which, for example, disk-shaped steel plates are laminated along the center axis oppose with respect to each other, where the opposing surfaces thereof are orthogonal to the revolving shaft.
On the opposing surface of the rotor yoke, a magnet for generating a magnetic field is disposed, for example, in circular shape (ring shape), and the magnet has magnetic poles (N-pole, S-pole) disposed alternately circumferentially thereof.
On the opposing surface on the stator yoke, there are disposed a plurality of teeth along the radial direction (in the directions of radii) with respect to the revolving shaft. The surfaces of the magnet and the teeth opposing each other are orthogonal to the revolving shaft, and the gap between the opposing surfaces is formed into a plane perpendicular to the revolving shaft.
In other words, in a axial gap motor, a magnetic circuit is formed between the rotor and the stator, and the rotor is rotated using an attraction force and a repulsion force of the rotor-side magnet with respect to the respective teeth. The repulsion force is generated by sequentially switching the magnetic fluxes generating the respective teeth corresponding to the N-pole and the S-pole of the rotor-side magnet via coils wound around the respective teeth of the stator.
However, in the dynamo-electric machine described above, since the switching of the magnetic poles performed every time the magnetic pole of the magnet facing the teeth is switched in association with rotation of the rotor is very rapid, a harmonic content may be contained in the induced voltage waveform generated by mixed magnetic fluxes.
Such harmonic content may change the induced voltage waveform from a sinusoidal waveform to the deformed shape, and thus generate a torque ripple, which may lead to uneven rotation of the rotor, and hence to vibrations and/or noise.
Regarding this point, JP-A-2001-57753 discloses a construction in which pulsation of motor torque is reduced by forming grooves by grinding boundaries between the respective adjacent magnetic poles out of the plurality of magnetic poles stuck on an iron core of the rotor.
However, in the construction disclosed in the JP-A-2001-57753, it is required that the plurality of magnetic poles be adhered respectively on the iron core of the rotor. Then all the boundaries between the adjacent magnetic poles must be ground after such adhesion. Therefore, assembly of the rotor is more complicated, and the number of components of the rotor is increased.